Added regex support to #add_rule (tests included).
Due to strange behavior in Sourcify, the /.../ literal syntax cannot
be used as a parameter; only %r{} or Regexp::new. There is a note
for this in the documentation for #add_rule.
Fixed issue mentioned in FIXME comment in RubyDNS::Server#match.
Changed 'block.class.name' to just 'block' in case/when clause.